A levelling valve of the type described above is known from German Patent Application No. DE 37 16 436 Al, the levelling valve having a height limitation. A control rod acting upon a double valve body of the inlet valve and the outlet valve is connected with a guiding member arranged slidingly and sealingly in a housing. The guiding member comprises a groove cooperating with an eccentric follower of an actuation drive. The actuation drive comprises a lever, a shaft rotatably arranged, and the eccentric follower. For height limitation purposes a hollow actuation rod is connected with the guiding member on the side opposed to the double valve body. The hollow actuation rod carries a vent seat to which an annular valve body is assigned, the valve body being spring loaded and suspended in the housing. The valve body cooperates with an inlet seat located in fixed relation there to in the housing so that in this way a closing valve is generated for a conduit leading to the bellows. Thus, the maximun suspension height of the vehicle is defined and limited. There is an assignment to the angle position of the lever of the actuation drive caused by the closing position, i.e. the position in which both the inlet valve and the outlet valve are closed at the same time. In general, a horizontal position of the lever of the actuation drive is assigned to the mentioned closing position in accordance with a first vehicle height. This means that the chassis of the vehicle during driving takes a first determined height in which the lever of the actuation drive is in a horizontal position and the closing position is reached on the inlet valve and the outlet valve so that the suspension bellows are neither aerated nor vented, but carry the chassis in the designed height. However, often it is useful to be able to attain a second vehicle height differing from the first vehicle height. This may be the case in order to adapt an inclined position of semitrailer to points on tractors having different heights. Another possibility of a second vehicle height is useful for busses. In such a second vehicle height the chassis of the bus may be lowered to make the entering of the bus easy for persons. In a third application it may be useful to have the chassis lowered to generate reduced drag. A levelling valve is known from FIG. 4 of DE 37 16 436 Al having the possibility to adjust alternatively to two different vehicle heights. For these purposes the groove in the guiding member into which the eccentric follower extends is provided with a large clearance so that the eccentric follower contacts the groove once on the one side of the groove or on the other side of the groove respectively. By this clearance the two different vehicle heights are defined. A control piston is connected in fixed manner with the guiding member and with the actuation rod extending downwardly in order to adjust alternatively to one of the two different vehicle heights. An aeratable control chamber is assigned to the control piston, the control chamber being positioned in the housing of the levelling valve. The aerated position of the control chamber is assigned to the second vehicle height, while the first vehicle height is reached by springs loading the control rod in case the control chamber is vented. It is a disadvantage that the control piston during aeration of the control chamber loads the guiding member and thus the control drive. Especially the eccentric follower extending into the groove of the guiding member is subjected to substantial wear reducing lifetime of the levelling valve. A further disadvantage is the different acting of the height limitation with respect to the first or the second adjusted vehicle height. If the second vehicle height is located above the first vehicle height the maximal stroke up to the stops for the chassis via the bellows must be assigned to the second vehicle height. However in this case the height limitation during adjustment of the first vehicle height is active i.e. the maximum stroke of the bellows cannot be used in the position of the first vehicle height.
German Patent No. DE 23 18 535 describes a levelling valve of a different type, in which the shaft of the actuation drive is extended and further elements are provided in parallel to the control rod for the inlet valve and the outlet valve, for example a second outlet valve having an enlarged cross section. Levelling valve of this kind may be provided with a height limitation also. On the other hand the adjustment of a second vehicle height is possible. The alternative adjustment of two different vehicle heights is described as a variation of a starting point or position. This variation of the starting position is performed in a similar manner as illustrated in FIG. 4 of DE 37 16 436 by the fact of providing a large clearance between the eccentric follower and the groove in the guiding member, which is bridged in the alternative adjustment of the two different vehicle heights.